Ice machines are widely used in restaurants and the like for producing ice, in the form of flakes, chips, cubes, etc. for use in beverages and for other uses relating to food and drink services. Generally, these ice machines include a refrigeration apparatus for freezing water supplied to the machine, a means for periodically removing, or "harvesting" ice from the freezing surface, and a cabinet or bin for storing the ice until it is needed.
In a typical ice making apparatus, water is brought in contact with a refrigerated surface, usually referred to as the evaporator, to be frozen. Freezing takes place for an interval of time, typically fifteen to twenty minutes, until the size of the ice cube is adequate. At this point, the harvesting operation takes place to remove the cubes from the evaporator. When harvested, the ice cubes typically fall off of the evaporator and are directed into an ice holding bin.
Ice making evaporators are typically constructed using stainless steel or nickel-plated copper. These materials are used because of their suitability for use with potable water and their heat transfer characteristics. Copper for example, is an excellent conductor of heat and therefore is well suited for use in ice machines. Stainless steel is also used extensively in ice making evaporators because of its non-rusting properties and suitability for contact with potable water. While these materials are well suited for use in ice machine evaporators, they can be expensive to use and fabricate.
An example of an ice making evaporator that is commercially available is provided in U.S. Pat. No. 4,458,503 to Kenneth L. Nelson. This patent describes an ice making evaporator consisting of a serpentine copper tube to which a series of formed, nickel-plated copper strips are attached. The entire assembly is placed into an injection mold and molded over with a plastic material. All of the copper tubing and portions of the copper strips are molded over with plastic. Other portions of the copper strips are left bare (free of plastic) to provide a good heat transfer path from the refrigerant to the water and ice. These bare portions of the evaporator plate provide the locations where the ice cubes will form.
Another example of a commercially available ice making evaporator is provided in U.S. Pat. No. 5,479,707 to Alvarez, et al. This patent describes an evaporator constructed from sheets of stainless steel which are stamped, punched and then welded together to create a flat-walled serpentine refrigerant passage. This stainless steel serpentine is placed into an injection mold and molded over with a plastic material to create ice cube formation sites of the desired shape. The stainless steel is left exposed in the locations where ice is to form so as to improve heat transfer. In this design the ice cubes form on these exposed areas, which are also the stainless steel walls of the refrigerant passage.
Both of the evaporator designs referenced above utilize relatively expensive tooling, processes and materials to create the evaporator assemblies.
A primary objective of this invention is to utilize materials and manufacturing processes which are inherently low in cost in order to substantially reduce the cost of an ice making evaporator.
Another primary objective of this invention is to optimize the heat transfer performance of the evaporator assembly through its ice forming geometry and by incorporating unique features to enhance heat transfer.
Another primary objective of this invention is to minimize the thermal mass of the evaporator assembly. Since an ice machine evaporator is constantly cycled between hot and cold temperatures, lowering the thermal mass of the assembly will result in less energy being needed to heat and cool the assembly between those temperatures.
Another primary objective of this invention is to provide a freezing surface which meets the ice machine sanitation requirements of the National Sanitation Foundation.
The present invention achieves these objectives utilizing a uniquely formed aluminum roll-bond type evaporator plate upon which is molded a grid of plastic ridges which form an array of ice cube forming sites on both sides of the plate. This plastic grid is comprised of thin vertical ridges and wider horizontal ridges. The vertical ridges act to separate horizontally-adjacent cube forming locations. The horizontal ridges act to separate vertically-adjacent cube forming locations and to cover the refrigerant passages of the roll-bond evaporator plate. Additional features not previously used in ice making evaporators or roll-bond evaporator plates are also incorporated into the present invention to improve heat transfer and make this configuration manufacturable.
The low cost of the aluminum evaporator plate, the low thermal mass of the assembly, the geometry of the ice cube forming locations and the additional heat transfer improvements incorporated in this design provide superior heat transfer performance and significantly lower cost than existing ice making evaporator designs.